The present invention relates to the field of hydraulic pumps. More particularly, the present invention relates to a means and method for varying the margin pressure or delta pressure across a load sensing valve in an open circuit pump system. The invention provides better operator control of working functions on equipment such as backhoes and the like.
Some backhoe manufacturers have sought an open circuit pump control system with a load sensing control valve that has a delta pressure across the valve which varies with the displacement of the pump. Thus, there is a need for a means and method to accomplish this in an open circuit application.
Therefore, a primary objective of the present invention is the provision of an open circuit pump system having a load sensing control valve and a variable orifice associated with the servo pressure conduit thereof such that the delta pressure or margin pressure across the load sensing valve varies based upon the fluid displacement of the pump.
Another objective of the present invention is the provision of a variable orifice located in the servo pressure conduit and defined by a gap formed between the housing and a servo piston slidable within the housing.
Another objective of the present invention is the provision of a servo piston having a longitudinal slot therein which has a depth that uniformly increases along the length of the servo piston so as to define a variable orifice area.
Another objective of the present invention is the provision of a servo piston having a slot whose depth varies uniformly along a straight tapered bottom surface.
A further objective of the present invention is the provision of a method of varying the fluid pressure differential across a load sensing valve in a variable displacement open circuit pump.
A further objective of the present invention is the provision of a pump system that is economical to produce, durable, and reliable in use.
These and other objectives will be apparent from the drawings, as well as the written description and claims which follow.